1. Field of the Invention
The present invention relates to an actuator unit that exerts force such as torque in response to an electric signal, and a multi-axis robot including the actuator unit, in particular, to an actuator unit that drives an articulated machine such as a robot, and a multi-axis robot.
More specifically, the present invention relates to an actuator unit that is applicable to joints, each movable along two or more axes, such as a hip joint, a knee joint, or an ankle joint of a legged mobile robot, and relates to a multi-axis robot. More specifically, the present invention relates to a biaxial actuator unit having two orthogonal axes which are easily movable, and relates to a multi-axis robot.
2. Description of the Related Art
A machine that performs human-like movement electrically or magnetically is referred to as “robot”. The term “robot” is derived from the Slavish word “ROBOTA (slave machine)”. In Japan, robots became popular at the end of the 1960s. Most of them were industrial robots such as manipulators and transfer robots aimed at automation or unmanned operations in manufacturing at factories.
Stationary robots fixedly installed at certain locations, such as robot arms, operate in only predetermined local workspaces, for example, for selecting and assembling parts. On the other hand, mobile robots, which flexibly move in a predetermined or a free path and operate in unlimited workspaces, can be agents for predetermined or any human tasks, or can provide various kinds of services in place of human beings, dogs, or other living beings. Legged mobile robots, among others, are superior to crawler or tire-wheeled robots in terms of being capable of climbing up and down stairs and ladders, riding over obstacles, and walking and running flexibly on both even and uneven grounds, although the postures and walking of the robots are unstable and difficult to be controlled.
Recently, research and development of the legged mobile robots have made progress and expectations of the practical applications are growing, which are pet robots simulating the body mechanism and motions of quadrupedal walking animals such as dogs and cats, or “man-shaped” or “man-type” robots referred to as “humanoid robots” designed based on the model of human body mechanics and motions.
Such legged mobile robots generally have a plurality of joints capable of moving along any axis by actuator motors. In addition, a servo control reproduces a desired motion pattern by detecting rotation and movements of the motors and then controls the postures.
A servo motor is commonly used to achieve flexible movement of the robot joints. This is because a servo motor is easy to operate and small-sized and has high torque and quick response. In particular, an AC servo motor, which is brushless and maintenance-free, is applicable to a joint actuator of a legged robot which preferably operates, for example, walks freely in an unmanned workspace. The AC servo motor has a permanent magnet in a rotor and a multi-phase coil (for example, a three-phase coil) in a stator and is designed to generate torque of the rotor from sine-wave magnetic flux distribution and sine-wave electric current.
Generally, the legged mobile robot has many joints. Accordingly, the servo motor that achieves the flexible movement of the joints must be designed and manufactured to be compact and high-performance. For example, a small gear-direct AC servo motor which has a one-chipped servo controller is already available (refer to, for example, Japanese Unexamined Patent Application Publication No. 2000-299970).
Referring to FIGS. 1A and 1B, in such an actuator unit, a power-supply and control-signal harness 2 extends from a body of the actuator 1. Additionally, an output shaft 3 coupled with the rotor of the actuator motor has only a mechanics for fixing a support structure.
As a result, the harness 2 must be designed to extend through a plurality of moving parts when a user or a designer develops a multi-axis robot using such actuator units.
Further, to develop the joints having two or three orthogonal axes, a complicated mechanical design using a belt and a linkage mechanism is required.
Furthermore, the production and the maintenance of the robot using the actuator units are not necessarily efficient.